This invention relates generally to medication infusion pumps particularly of the type for implantation directly into the body of a patient, and for programmed operation to deliver medication to the patient. More specifically, this invention relates to an improved implantable infusion pump having a relatively simple flow sensor operable with minimum power requirements to monitor and verify medication outflow to the patient in response to infusion pump operation.
Medication infusion pumps are generally known in the art for use in delivering a selected medication to a patient in a scheduled or preprogrammed manner. In recent years, such infusion pumps have been developed in compact form adapted for direct implantation into the body of a patient, and to deliver a specific medication such as insulin to the patient in discrete doses over an extended time period. An implanted infusion pump of this general type includes an internal medication chamber for receiving and storing a supply of the selected medication in liquid form, with the medication being subjected to a predetermined storage pressure to ensure accurate and repeatable delivery conditions through the use of a miniature dispensing pump and associated programmed control means. In many cases, the medication storage pressure is less than ambient body pressure to prevent undesired leakage of the medication from the medication chamber into the body of the patient, and thereby positively prevent accidental overdose during certain failure modes. For one illustrative example of an implanted medication infusion pump of this general type, see U.S. Pat. No. 4,573,994.
While such implantable infusion pumps have constituted a major step forward in reliable and convenient administration of certain medications, certain failure mode conditions may nevertheless occur wherein the desired medication is not in fact delivered to the patient. For example, the medication is typically delivered from the dispensing pump through a small bore catheter to a selected administration site within the body of the patient, but nondelivery of the medication can occur despite proper pump operation in the event that the catheter becomes clogged. Alternately, although rare, medication nondelivery can be the result of mechanical pump failure. In the past, implantable infusion pumps have not included satisfactory means for verifying or confirming actual medication outflow to the patient in response to infusion pump operation.
There exists, therefore, a significant need for an improved implantable infusion pump, particularly with respect to providing means for monitoring and verifying actual delivery of the selected medication to the patient in response to operation of the dispensing pump. The present invention fulfills these needs and provides further related advantages.